This invention relates to a method of effecting venipuncture in the human body, for such purposes as drawing blood and making intravenous injections and infusions. More particularly, the invention relates to a venipuncture method employing an enantiotropic cholesteric liquid crystalline phase material for vein location.
Conventional venipuncture methods as long practiced have suffered from disadvantages and shortcomings which affect the patient in varying degrees of seriousness. With increasing proportions of less-qualified technicians, who may be trained only in blood-drawing, difficulties encountered during venipuncture for out-patient and in-patient blood drawing, blood banking, and I.V. therapy have increased. The problems are minimized when the veins are readily visible and/or palpable. However, it happens frequently that the vein locations are not readily visible or palpable, and where the veins are palpable but not visible, it may be difficult to determine the best site for needle insertion. Lacking in visibility, and even after application of a tourniquet, it frequently happens that the technician misses the vein with a needle and must probe until the needle hits the vein, or multiple insertions of the needle are required, which are painful procedures. In certain procedures, such as in an intranvenous pylogram, in which a radioopaque contrast media (X-ray dye) is injected into the vein, an improper injection can cause subcutaneous skin damage. Problems are encountered when patients require frequent blood drawing during long hospitalization or extensive testing, and repeated venipuncture at the same site causes bruising, edema, scarring, and/or hardening of the vein and surrounding tissues. The veins then become less visible and palpable, venous blood flow is reduced, and the needle does not penetrate the scarred or hardened tissue readily. Under such circumstances, and also when patients require repeated intravenous administration during long I.V. therapy or due to complications, new injection sites may be required and often are difficult to find.
There is, therefore, a need for a rapid method of greater reliability for locating veins in the human body, in hospitals, clinics and laboratories, preparatory to drawing blood or making intravenous injections or infusions. It would be advantageous to provide a venipuncture method which overcomes the prior difficulties by indicating the best vein site and direction for needle insertion and, even more advantageously, providing information about the depth of the vein and its blood blow.
Cholesteric liquid crystalline phase materials, also referred to as cholesteric liquid crytals, their technology and applications are reviewed in the book by Peter L. Carroll entitled "Cholesteric Liquid Crystals," June, 1973 (Ovum Ltd., London). The materials, hereinafter referred to at times for convenience simply as "liquid crystals," are a class of compounds that display a cholesteric mesophase within certain temperature limits. The cholesteric mesophase is a state of matter intermediate in molecular ordering between a crystalline solid and an isotropic liquid. In general, the materials are colorless in their solid and isotropic liquid states, assuming the coloration of their background or of light-absorptive materials added thereto. When liquid crystals are in the cholesteric mesophase, and ordinary white light is directed at the material, the light is separated essentially into two components, one of which is transmitted and one of which is scattered or reflected. The scattered light gives the material an iridescent color, which depends upon the material, the temperature, and the angle of the incident light beam.
Prior patents relating to thermal color-responsive or temperature-sensitive cholesteric liquid crystal compositions and their use in applications where temperature is to be measured or a temperature pattern is to be observed include U.S. Pat. Nos. 3,114,836, 3,441,513 and 3,533,399, the latter patent having to do with the production of visible patterns corresponding to skin temperature patterns in human beings. Reports on the application of liquid crystal thermography to examination of the body include an article by Davison, Ewing, Fergason, Chapman, Can, and Voorhis, "Detection of Breast Cancer by Liquid Crystal Thermography," Cancer, Vol. 29, No. 5, page 1123, May, 1972, and an article by Davison, Ewing, Sayat, Mulla, and Fergason, "Liquid Crystal Thermographic Placental Location," Obstetrics and Gynecology, Vol. 42, No. 4, page 574, October, 1973.
In order to improve color contrast, the liquid crystals commonly are applied to and viewed against an absorptive, particularly a black background, which serves to absorb the transmitted light. Alternatively, absorptive, generally black particulate material is admixed with the liquid crystals, so as to absorb the transmitted light while not interfering excessively with the intensity of the scattered light. As an additional alternative, it has been proposed to incorporate black or colored dyes in the liquid crystal compositions.
The most common technique for applying liquid crystals to measure or map temperatures, as on a surface of the body, is to first blacken the surface with an aqueous, oil-impervious black paint, then apply liquid crystals from a solution by brushing or spraying. Liquid crystals dispersed in films and having a black backing or black filler for absorbing transmitted light have been applied to surfaces, including body skin, for measuring temperatures and for thermal mapping. Encapsulated liquid crystals are employed in a laminated article including a black background for locating veins in the body, in a venipuncture method disclosed in U.S. Pat. No. 3,998,210.